1. Field of the Invention
Embodiments of the invention generally relate to fluid catalyst injection systems for fluid catalyst cracking units.
2. Background of the Related Art
Fluid catalyst cracking units (FCCU) are commonly used in petroleum refining to break long chain hydrocarbons present in crude oil and to adjust the product mix recovered at the distiller. A main catalyst is generally introduced into the FCCU by a catalyst injection system which periodically meters out catalyst for injection over a predefined period of time. Such injection systems are available from Intercat, Inc., located in Sea Girt, N.J. Other examples of conventional injection systems are described in U.S. Pat. No. 5,389,236, issued Feb. 14, 1995, which is incorporated by reference in its entirety.
In addition to the main catalyst, it is often beneficial to inject other catalysts into the FCCU to further influence the refining process. For example, some catalyst are formulated to control certain types of emissions, such as the amount of sulfur- and nitrogen-containing compounds present in refinery emissions. Other catalysts may be formulated to influence the product mix recovered in the distiller. For example, catalyst may be formulated to produce more diesel fuel relative to gasoline or to increase the amount of liquid petroleum gas produced, among others. As these injection systems are typically supported on a separate foundation and hard pipe connected to the FCCU, the flexibility of the refiner to rapidly add an additional catalyst injection system is very limited.
For example, the time required to plan and install a new catalyst injection system may prevent the refiner from taking advantage of market conditions favorable to a certain product mix not achievable using the catalyst injection systems currently coupled to the FCCU. The difficulty in providing quick process adjustment through the injection of additional catalyst in a new catalyst injection system also hampers the ability of the refiner to quickly adjust refinery emissions due to changes in regulations, differences in the chemical make-up of crude oil or process equipment failure. Furthermore, as catalyst injection systems are expensive to install, it is undesirable to have unused catalyst injection systems stationed online as a precaution against any unanticipated need for process control.
Additionally, conventional pressure regulation systems utilized to control the pressures with in a catalyst injection system are not stable, causing the total amount of gas within the chamber to fluctuate. This change in mass of gas within the catalyst injection system results in erroneous weight calculations of catalyst dispensed into the FCCU, leading to less than optimum process control.
Therefore, there is a need for an improved catalyst injection system.